Assessment of cardiac iron by MRI susceptometry and R2* in patients with thalassemia

Abstract

An MRI cardiac magnetic susceptometry (MRI-CS) technique for assessing cardiac tissue iron concentration based on phase mapping was developed. Normal control subjects (n=9) and thalassemia patients (n = 13) receiving long-term blood transfusion therapy underwent MRI-CS and MRI measurements of the cardiac relaxation rate R2*. Using MRI-CS, subepicardium and subendocardium iron concentrations were quantified exploiting the hemosiderin/ferritin iron specific magnetic susceptibility. The average of subepicardium and subendocardium iron concentrations and R2* of the septum were found to be strongly correlated (r=0.96, p<0.0001), and linear regression analysis yielded CIC (μg Fe/g wet tissue ) = (6.4 ± 0.4) · R2* septum (s -1 ) -(120 ± 40). The results demonstrated that septal R2* indeed measures cardiac iron level.

Hepatic Glycosphingolipid Deficiency and Liver Function in Mice

“…Ignoring effects from field inhomogeneity, which in the liver of a healthy subject is on the order of 0.1–0.2 ppm/cm (34), the susceptibility Δχ is calculated from the field map by: where Δ f is the mean change in the field between two regions, θ is the angle between the field measurement and the static field (θ was set to 90° in this work since all images were acquired in the transverse plane), and S hf is the orientation‐independent shift term set to −0.133 from results of previous studies (21, 35, 36). Also note that the change in phase, Δϕ, can be used with an image at TE where: …”

“…This method, typically performed by a superconducting quantum interference device (SQUID), has also been calibrated with biopsy, but the cost of the equipment has limited its clinical use. Some studies have also used MR to measure the susceptibility via field mapping as an additional acquisition to the mGRE acquisition (21–23). LIC values may be more accurately estimated by susceptometry methods than by R methods, as the former is a direct measure of susceptibility due to iron content (21).…”

“…Some studies have also used MR to measure the susceptibility via field mapping as an additional acquisition to the mGRE acquisition (21–23). LIC values may be more accurately estimated by susceptometry methods than by R methods, as the former is a direct measure of susceptibility due to iron content (21). However, the absolute phase for MR susceptometry methods is difficult to obtain because of factors such as flow, motion, and phase variations (22).…”

On T2* Magnetic Resonance and Cardiac Iron

“…12,13,14 In the liver, T2* correlates well with biopsy iron concentration. 8,15 Although the relationship between T2* and cardiac iron can be inferred from first principles, animal models, 16 and the liver data, there is limited direct information on cardiac calibration of T2* in humans, 17,18 and the inherent limitations associated with endomyocardial biopsy prevent in vivo calibration. 19 We therefore initiated a project to calibrate cardiac T2* against chemically assayed tissue iron concentration in ex-vivo human hearts and determine its cardiac distribution.…”

Noninvasive MRI-Based Liver Iron Quantification: Methodic Approaches, Practical Applicability and Significance

“…The local magnetic field strength, which depends on the iron content, can be determined from a corresponding analysis of the MRI signals [45]. A comparison with reference tissue makes it possible to determine the magnetic susceptibility of the tissue in question, i. e., the amplification of the external magnetic field primarily caused by the iron that is present [46].…”